This invention relates to a data-transmission system and more particularly to a data-transmission system using a continuous automatic repeat request (abbreviated as "ARQ") system.
Known systems for controlling errors in data transmission include the ARQ type in which an error concerning data blocks delivered from a transmitter are detected by a receiver, and the transmitter is demanded to retransmit the data block.
With one form of the ARQ type which is referred to as "a continuous ARQ system," data blocks are continuously sent forth from the transmitter to the receiver. Where an erroneous data block is detected by the receiver, then the transmitter retransmits to the receiver the data block corresponding to the erroneous data block and the succeeding series of data blocks.
With one of the known data-transmission systems, data blocks are sent forth from the transmitter to the receiver in succession to a plurality of synchronization codes each formed of a plurality of bits in order to establish a block synchronization between the transmitter and receiver. With this prior art data-transmission system, synchronization can not be established, unless any of the plural synchronization codes is detected by the receiver. In such case, the receiver fails to be supplied with any data.
Where, with the continuous ARQ system, transmission channels are of high quality, a higher data rate is more efficient due to transmission time being shorted accordingly. Where, however, the transmission channels are degraded, then a higher data rate will unavoidably make it necessary to retransmit the same data more often than otherwise. On the whole, therefore, a longer transmission time will have to be consumed than when a data rate is low.